Question

Pyrolusite is \(\mathrm{MnO}_{2}\) used to prepare \(\mathrm{KMnO}_{4}\). Steps are, \(\mathrm{MnO}_{2} \stackrel{1}{\longrightarrow} \mathrm{MnO}_{4}^{2-} \longrightarrow \mathrm{MnO}_{4}^{-}\). Steps \(\mathrm{l}\) and \(\mathrm{II}\) are respectively : (1) fuse with \(\mathrm{KOH} /\) air and electrolytic oxidation. (2) fuse with \(\mathrm{KOH} / \mathrm{KNO}_{3}\) and electrolytic reduction. (3) fuse with conc. \(\mathrm{HNO}_{3} /\) air and electrolytic reduction. (4) dissolve in \(\mathrm{H}_{2} \mathrm{O}\) and oxidation.

Short answer

Option 1 is correct: fuse with \(\text{KOH} \) / air and electrolytic oxidation.

Step-by-step solution

- Understanding the Reaction Sequence

Recognize that \(\text{MnO}_2\) is converted to \(\text{MnO}_4^{2-}\) in the first step, and \(\text{MnO}_4^{2-}\) is further converted to \(\text{MnO}_4^{-} \) in the second step.

- Identify Step I

Determine the correct reagent to fuse with \(\text{MnO}_2 \) to get \(\text{MnO}_4^{2-} \): Fusing \(\text{MnO}_2 \) with \(\text{KOH} \) in the presence of air forms \(\text{K}_2\text{MnO}_4 \), which contains \(\text{MnO}_4^{2-} \).

- Identify Step II

Recognize the next step to convert \( \text{MnO}_4^{2-}\) to \(\text{MnO}_4^{-}\): An electrolytic oxidation process is required, where \(\text{K}_2 \text{MnO}_4\) is converted to \(\text{KMnO}_4\).

- Combine Steps I and II

Combine the information: The overall conversion of \( \text{MnO}_2 \) to \( \text{KMnO}_4 \) involves first fusing with \( \text{KOH} \) and air, and then performing electrolytic oxidation.

- Choose the Correct Option

From the given options, identify the one that matches the described steps: Option 1 - fuse with \(\text{KOH} \) / air and electrolytic oxidation.

Key concepts

Chemical Reactions

Chemical reactions are the processes where substances change into new substances with different properties. When preparing \(\text{KMnO}_4\), we start with pyrolusite \(\text{MnO}_2\). This substance undergoes a series of chemical reactions to transform into potassium permanganate (\(\text{KMnO}_4\)).

First, we fuse \(\text{MnO}_2\) with potassium hydroxide (KOH) in the presence of air to get potassium manganate (\(\text{K}_2\text{MnO}_4\)). This is a vital intermediate compound in the preparation of \(\text{KMnO}_4\).

After forming potassium manganate, we need to change it into \(\text{KMnO}_4\) through a process called electrolytic oxidation. During this step, \(\text{MnO}_4^{2-}\) ions in potassium manganate get oxidized to \(\text{MnO}_4^{-}\) ions, creating the final product: potassium permanganate.

This series of chemical reactions highlights the importance of specific conditions and reagents in forming new substances.

Inorganic Chemistry

Inorganic chemistry is the branch of chemistry dealing with inorganic compounds, usually those without carbon. Preparing \(\text{KMnO}_4\) involves multiple steps involving inorganic compounds such as \(\text{MnO}_2\) and KOH.

Pyrolusite, which is \(\text{MnO}_2\), is a naturally occurring mineral often used as a starting material in various inorganic chemical processes. In the preparation of potassium permanganate, we first use KOH to facilitate forming potassium manganate. This fusion process requires specific conditions, such as the presence of oxygen from air, to ensure the correct chemical reaction.

The next key element is electrolytic oxidation. This step is another classic example of inorganic chemistry at work. By applying an electric current, the ions in potassium manganate are oxidized, transforming them into the permanganate form. This showcases how controlled chemical techniques can manipulate specific ions to synthesize desired inorganic compounds.

Electrolytic Oxidation

Electrolytic oxidation is a process where electrical energy is used to drive a non-spontaneous oxidation reaction. In the creation of \(\text{KMnO}_4\), this step is crucial.

Once we have potassium manganate (\(\text{K}_2\text{MnO}_4\)), we place it in an electrolytic cell. In this setup, an electric current is passed through the solution. The current causes the \(\text{MnO}_4^{2-}\) ions to lose electrons (be oxidized), forming the \(\text{MnO}_4^{-}\) ions present in potassium permanganate.

Electrolytic oxidation was chosen for this step because it precisely controls the oxidation state of manganese, ensuring the production of \(\text{KMnO}_4\). This control is essential because without it, unwanted by-products could form, making the process less efficient.

Overall, electrolytic oxidation is a powerful tool in inorganic chemistry for making specific adjustments to the oxidation states in compounds, demonstrating its importance in various industrial and laboratory applications.